Non-small cell lung carcinoma (NSCLC) is the most prevalent type of lung cancer and has a poor 5-year survival rate of only 15% due to metastatic disease at diagnosis. Better understanding of the mechanisms of metastasis will increase patient survival by providing novel targets for cancer therapeutics. One molecule that has been implicated in leading to an increase in metastatic potential is liver kinase B1 (LKB1). LKB1 is a serine threonine kinase involved in regulating cell metabolism via signaling through AMP kinase. Independently of the kinase function, LKB1 also is a known cell polarity regulator in normal and cancerous cells. In NSCLC, LKB1 is the third most commonly mutated gene, and its loss causes increased metastatic disease in animal models. The mechanism for how LKB1 loss impacts cancer cell migration and metastasis is largely unknown. Our preliminary data using 3-D lung cancer spheroids show that LKB1 may serve as a regulator of a molecular switch between differing invasion mechanisms, as its loss results in a mesenchymal to amoeboid transition. This switch may provide a migratory advantage to cells through aberrant polarity signaling and ultimately provide LKB1-depleted cells increased plasticity in motility through the tumor microenvironment. Therefore, we will test the central hypothesis that LKB1 loss disrupts normal cell polarity and thereby provides cells an invasive advantage while navigating the microenvironment. To test this, we will determine: 1) the mechanism by which LKB1 regulates a molecular switch between mesenchymal and amoeboid phenotypes in 3-D invasion and 2) if LKB1 loss enhances tumor cell plasticity to facilitate invasion through the microenvironment. In Aim 1, we will use live cell imaging to image invasion from a 3-D spheroid in real time to observe and analyze invasive phenotype, allowing for study of early events in the metastatic cascade. Specifically, we will determine which specific region(s) of LKB1 is vital for its regulatin of the switch between mesenchymal and amoeboid invasion phenotypes. We will also analyze if LKB1 loss results in a loss of cell polarity regulation through aberrant Rho GTPase activity. In Aim 2, we will utilize our clinically relevant KrasG12DLkb1fl/fl mouse model, which we have already re-created, to study the impact of LKB1 loss on motility and metastasis. This mouse model which will allow us to analyze via ex vivo lung tumor slices if LKB1-depletion results in increased plasticity of motility phenotype through defective polarity signaling, thus providing an invasive advantage when navigating the microenvironment. Additionally, we will use these mice to determine the impact of pharmacological inhibition of mesenchymal and/or amoeboid migration on metastasis in LKB1-depleted mice. This work will advance our understanding of LKB1 biology and its relationship to regulating motility through the microenvironment. Moreover, it will provide insight into the basic cellular mechanisms guiding lung cancer invasion with the ultimate goal of developing therapeutics for LKB1 mutant patients.